The present invention relates, in general, to access doors for pressurized air chambers such as boiler windboxes and, more particularly, to a new and useful access door with a safety catch feature which alerts the boiler operator that the windbox is under pressure.
Windboxes are used in boilers to supply preheated air. U.S. Pat. No. 3,479,994 discloses a wraparound windbox for this purpose. Another windbox arrangement is disclosed in U.S. Pat. No. 3,781,162.
FIGS. 1 and 2 are respective front and side elevation views of a known access door for boilers and comprises a frame 10 defining an opening into the boiler space, and a door 12 connected to the frame at a hinge 14 for movement of the door on the frame between a closed position, covering the opening, and an open position, spaced away from the opening (not shown). A C-shaped latch 16 having a heat dissipating handle 18, is pivotally mounted, at pins 20, to opposite sides of the door 12. To lock the door in the closed position shown in FIGS. 1 and 2, latch 16 is pivoted in the direction of arrow A so that a pair of hooks 22, on opposite sides of the latch, engage a pair of trunnions or posts 24 extending from opposite sides of the housing 10. If a chamber outfitted with the door of FIGS. 1 and 2 is under pressure, door 12 will open rapidly once latch 16 is moved in a direction opposite to arrow A, for unlocking the door.
The air within the windbox is normally under elevated pressure and at a temperature of around 400.degree. F. Under these conditions, access doors into the windbox need not be cooled. A dangerous condition may arise, however, when a boiler operator attempts to open an access door to a windbox, which is under pressure, without stepping aside as gusts of hot air will blow through the open door.
A variety of furnace access doors are known which include cooling and specialized latches. Cooling is necessary since combustion gases within the furnace may be as high as 2000.degree. F. See, for example, U.S. Pat. Nos. 2,545,886; 2,775,216; 2,920,585; and 3,055,321.
A need remains for a windbox access door construction which provides the operator with a warning that the windbox is under pressure, and a mechanism to prevent the door from swinging open rapidly under these conditions.